Imprint mask, method for manufacturing the same, and method for manufacturing semiconductor device

ABSTRACT

According to one embodiment, an imprint mask includes a quartz plate. The quartz plate has a plurality of concave sections formed in part of an upper surface on the quartz plate, and impurities are contained in a portion between the concave sections in the quartz plate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2010-121446, filed on May 27,2010; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an imprint mask, amethod for manufacturing the same, and a method for manufacturing asemiconductor device.

BACKGROUND

Photolithography has hitherto been used for manufacturing semiconductordevices. However, with miniaturization of the semiconductor devices,photolithography is becoming insufficient in resolving power, andpattern formation is thus becoming difficult. Hence, nanoimprinting hasrecently come to be used in place of photolithography.

In nanoimprinting, concavities and convexities are formed by selectivelyremoving the surface of a quartz substrate, a pattern (device pattern)obtained by inverting a resist pattern desired to be formed, and analignment mark for alignment are formed, and thus an imprint mask isproduced. Then, an ultraviolet cure resist material is applied on thesubstrate to be processed, and the imprint mask is pressed onto thisresist material. Next, while the imprint mask is held pressed, theresist material is irradiated with ultraviolet rays through the imprintmask, to be cured. In this manner, the device pattern formed in theimprint mask is transferred to the resist material, to form the resistpattern. In nanoimprinting, since there are fewer factors of variationsin focus depth, aberration, exposure, and the like which have beenproblems with conventional photolithography, once one imprint mask isproduced, a large number of resist patterns can be formed in anextremely simple and accurate manner.

Incidentally, manufacturing of the semiconductor device includes aprocess of forming a new pattern on a substrate previously formed with apattern. In the case of using nanoimprinting for such a process, it isnecessary to perform alignment of the imprint mask with respect to thesubstrate with high accuracy. This alignment is performed by overlappingan alignment mark formed in the imprint mask on an alignment mark formedon the substrate, while observing the marks with visible light.

However, since a refractive index of quartz as the material for theimprint mask with respect to the visible light is almost equivalent to arefractive index of the ultraviolet cure resist material with respect tothe visible light, when the imprint mask is pressed onto the resistmaterial and the resist material gets into the concave section of thealignment mark, the alignment mark becomes invisible. There has thusbeen a problem in that the alignment cannot be performed with sufficientaccuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view illustrating an imprint mask according to a firstembodiment;

FIG. 2 is a plan view illustrating an alignment mark region shown inFIG. 1;

FIG. 3 is a cross-sectional view along a line A-A′ shown in FIG. 2;

FIGS. 4A to 5C are process cross-sectional views illustrating a methodfor manufacturing the imprint mask according to the embodiment;

FIGS. 6A to 7C are process cross-sectional views illustrating a methodfor manufacturing a semiconductor device according to the embodiment;

FIG. 8 is a graph with a dose amount of the gallium ions taken on thehorizontal axis and a refractive index of the visible light and atransmittance of the ultraviolet ray taken on the vertical axes,illustrating the relation between an introduction amount of gallium andoptical characteristics of the quartz plate;

FIG. 9 is a graph with an acceleration voltage of the ions taken on thehorizontal axis and an implantation depth of the ions taken on thevertical axis, illustrating the relation between the accelerationvoltage of the ions and the implantation depth in the quartz;

FIG. 10 is a cross-sectional view illustrating an alignment mark regionof an imprint mask according to a second embodiment;

FIGS. 11A to 11D are process cross-sectional views illustrating a methodfor manufacturing the imprint mask according to the second embodiment;

FIG. 12A is a cross-sectional view illustrating a sample of the testexample, and FIG. 12B is a graph with a depth of the chromium film fromthe upper surface taken on the horizontal axis and a galliumconcentration taken on the vertical axis, illustrating a galliumconcentration profile along a straight line B shown in FIG. 12A

FIG. 13 is a cross-sectional view illustrating an alignment mark regionof an imprint mask according to the embodiment;

FIGS. 14A to 14D are process cross-sectional views illustrating a methodfor manufacturing an imprint mask according to a third embodiment;

FIG. 15A is a sectional view illustrating a sample of the test example,and FIG. 15B is a graph with a depth of the chromium film from the uppersurface taken on the horizontal axis and an atomic concentration ratiotaken on the vertical axis, illustrating a profile of a compositionalong a straight line C shown in FIG. 15A;

FIGS. 16A to 16E are process cross-sectional views illustrating a methodfor manufacturing the imprint mask according to a fourth embodiment; and

FIGS. 17A to 17C are process cross-sectional views illustrating a methodfor manufacturing the imprint mask according to a fifth embodiment.

DETAILED DESCRIPTION

In general, according to one embodiment, an imprint mask includes aquartz plate. The quartz plate has a plurality of concave sectionsformed in part of an upper surface on the quartz plate, and impuritiesare contained in a portion between the concave sections in the quartzplate.

In general, according to another embodiment, an imprint mask includes aquartz plate. The quartz plate has a device region and an alignment markregion set in the quartz plate, and a refractive index of light in thealignment mark region is different from a refractive index in the deviceregion.

In general, according to still another embodiment, a method is disclosedfor manufacturing an imprint mask. The method can include forming apattern made of a metal on a quartz plate. The method can includeetching the quartz plate using the pattern as a mask. In addition, themethod can include introducing impurities into at least a part of anetched region in the quartz plate. An introduction depth of theimpurities is made smaller than a depth of the etching.

In general, according to still another embodiment, a method is disclosedfor manufacturing an imprint mask. The method can include forming apattern made of a metal on a quartz plate. The method can includeintroducing impurities into at least a part of the quartz plate usingthe pattern as a mask. In addition, the method can include etching atleast a region in which the impurities have been introduced in thequartz plate, using the pattern as a mask. The depth of the etching ismade larger than an introduction depth of the impurities.

In general, according to still another embodiment, a method is disclosedfor manufacturing a semiconductor device. The method can includearranging a resist material on a substrate. The method can includepressing an imprint mask, in which a device pattern and an alignmentmark are formed on an under surface of the imprint mask, onto a resistmaterial, while performing alignment with respect to the substrate byuse of the alignment mark. The method can include curing the resistmaterial, while pressing the imprint mask, to form a resist pattern madeof the resist material. The method can include separating the imprintmask from the resist pattern. In addition, the method can includeperforming processing on the substrate using the resist pattern as amask. The imprint mask includes a quartz plate, the alignment mark isformed with a plurality of concave sections, and impurities arecontained in a portion between the concave sections.

Various embodiments will be described hereinafter with reference to theaccompanying drawings.

First, a first embodiment is described.

FIG. 1 is a plan view illustrating an imprint mask according to theembodiment, FIG. 2 is a plan view illustrating an alignment mark regionshown in FIG. 1, and FIG. 3 is a cross sectional view along a line A-A′shown in FIG. 2.

It is to be noted that in FIG. 2, concave sections are shown by beinghatched for the sake of simplicity of the drawing. Further, thesedrawings are schematic, and a ratio of dimensions of each section is notnecessarily consistent with that of an actual product. This also appliesto later-mentioned other drawings.

As shown in FIG. 1, an imprint mask 1 according to the embodimentincludes a quartz plate 10. The quartz plate 10 is made of a singlecrystal of silicon dioxide (SiO₂), and has a plate-like shape, which isfor example a square plate-like shape. It is to be noted that arefractive index of quartz with respect to visible light is about 1.4. Arectangular device region Rd is set in a central portion of the imprintmask 1, and a frame-like peripheral region Rs is provided on theperiphery of the device region Rd. Further, in the peripheral region Rs,alignment mark regions Ra are set at one or more locations, which arefor example four locations. The shape of the alignment mark region Rais, for example, square. One example is that the quartz plate 10 has athickness of several mm and a one-side length of 152 mm, the deviceregion Rd has a one-side length of 26 mm and the other-side length of 33mm, and the alignment mark region Ra has a one-side length of 0.5 mm(500 μm).

As shown in FIGS. 2 and 3, in the alignment mark region Ra, a pluralityof concave sections 11 is formed in the upper surface of the quartzplate 10, and a portion between the concave sections 11 in the quartzplate 10 is a convex section 12. Seen from above, namely seen in adirection vertical to the upper surface of the quartz plate 10, theconcave section 11 and the convex section 12 have square shapes, forexample, and are arranged in a checked pattern. That is, the concavesections 11 and the convex sections 12 are alternately arranged alongmutually orthogonal two directions. Further, the concave section 11 andthe convex section 12 each have a one-side length of 2 μm, for example.Moreover, a depth of the concave section 11, namely a height of theconvex section 12 or namely a distance between an upper surface 12 a ofthe convex section 12 and a bottom surface 11 a of the concave section11, is 50 nm, for example. The concave sections 11 and the convexsections 12 constitute an alignment mark 13.

Further, gallium (Ga) is contained as impurities in the convex section12, namely the portion between the concave sections 11. This gallium isintroduced by being ion-implanted from above. Thereby, a galliumdiffusion layer 16 is formed inside the convex section 12. The galliumdiffusion layer 16 is a layer which is formed of quartz as a basematerial and contains gallium. In a thickness direction of the quartzplate 10, a concentration of gallium in the convex section 12 and aregion immediately thereunder is normally distributed, and a peak of itsconcentration profile is located inside the convex section 12. Forexample, this peak is located at the same height as the center of theside surface of the convex section 12 in the thickness direction. Forexample, when the convex section 12 has a height of 50 nm, a peak of theconcentration profile of gallium is located 25 nm under the uppersurface 12 a of the convex section 12.

Further, gallium is also contained in a portion corresponding to theregion immediately under the concave section 11 in the quartz plate 10,to form the gallium diffusion layer 17. As is the gallium diffusionlayer 16, the gallium diffusion layer 17 is also a layer which is formedof quartz as a base material and contains gallium. A concentrationdistribution of gallium in the gallium diffusion layer 17 is similar tothat in the gallium diffusion layer 16. That is, the concentration ofgallium in the gallium diffusion layer 17 is normally distributed withrespect to the thickness direction, and when the convex section 12 has aheight of 50 nm, a peak of a concentration profile of gallium in thegallium diffusion layer 17 is located 25 nm under the bottom surface 11a of the concave section 11. The gallium diffusion layers 16 and 17 arepart of the quartz plate 10, and integrally formed with portions otherthan the gallium diffusion layers 16 and 17 in the quartz plate 10.

Meanwhile, in the device region Rd of the imprint mask 1, a devicepattern 15 (cf. FIG. 6) is formed in the upper surface of the quartzplate 10. Although the device pattern is also made up of concavesections formed in the upper surface of the quartz plate 10, the concavesections constituting the device pattern are finer than the concavesections 11 constituting the alignment mark, and each have a width ofthe order of 15 to 20 nm. It is to be noted that a depth of the concavesection in the device pattern is equivalent to the depth of the concavesection 11 in the alignment mark, and is 50 nm, for example.

When the quartz plate contains the impurities, the refractive index oflight differs as compared with the case that the impurities are notcontained. When the quartz plate contains gallium, the refractive indexto the visible light becomes larger. For this reason, a refractive indexof light in the alignment mark region Ra is higher than that in thedevice region Rd in the imprint mask 1. Further, when the quartz platecontains gallium, transmittances of the visible light and ultravioletray become low as compared with the case that gallium is not contained.Therefore, in the imprint mask 1, the transmittance of light in thealignment mark region Ra is lower than that in the device region Rd withrespect to the thickness direction of the quartz plate 10.

Next, a method for manufacturing an imprint mask according to theembodiment is described.

FIGS. 4A to 4D and FIGS. 5A to 5C are process sectional viewsillustrating the method for manufacturing the imprint mask according tothe embodiment.

It is to be noted that FIGS. 4A to 4D and FIGS. 5A to 5C show only partof an alignment mark region. This also applies to later-mentioned FIGS.11A to 11D, 14A to 14D, 16A to 16E, and 17A to 17C.

First, as shown in FIG. 4A, the quartz plate 10 is prepared. A chromiumfilm 21 with a film thickness of about several nm is then formed on theupper surface of the quartz plate 10 by sputtering, for example. Next,an electron-beam resist film 22 is formed on the chromium film 21 byapplication method, for example. Subsequently, electric-beam drawing isperformed by selectively irradiating the electron-beam resist film 22with electron beams EB, so as to draw a device pattern and an alignmentmark.

Next, as shown in FIG. 4B, the electron-beam resist film 22 isdeveloped. Thereby, the portion irradiated with the electron beams inthe electron-beam resist film 22 is removed, and the electron-beamresist film 22 is patterned.

Next, as shown in FIG. 4C, dry etching is performed with the patternedelectron-beam resist film 22 used as a mask and chlorine (Cl₂) gas andoxygen (O₂) gas, for example, used as etching gas, to selectively removethe chromium film 21. Thereby, the chromium film 21 is patterned so asto have the same pattern as the electron-beam resist film 22.

Next, as shown in FIG. 4D, the electron-beam resist film 22 is removed.

Next, as shown in FIG. 5A, dry etching is performed with the patternedchromium film 21 used as a mask and fluorine-based gas such as methanetetrafluoride (CF₄) gas used as etching gas, to etch the quartz plate10. Thereby, the quartz plate 10 is selectively removed, to form aconcave section with a depth of, for example, 50 nm in the upper surfaceof the quartz plate 10. This results in formation of the device patternand the alignment mark in the upper surface of the quartz plate 10. Itis to be noted that at this time, in the alignment mark region Ra, theportion between the concave sections 11 in the quartz plate 10 is theconvex section 12. Thereafter, the device pattern and the alignment markare inspected and corrected.

Next, as shown in FIG. 5B, the chromium film 21 is removed.

Next, as shown in FIG. 5C, gallium ions are implanted from above intothe alignment mark region Ra (cf. FIG. 1) of the quartz plate 10. Atthis time, an implantation depth of gallium is made smaller than a depthof the etching into the quartz plate 10 shown in FIG. 5A. Thereby,gallium is introduced into the convex section 12 to form the galliumdiffusion layer 16, while gallium is also introduced into the regionimmediately under the concave section 11, to form the gallium diffusionlayer 17. An acceleration voltage at the time of implanting the galliumions is, for example, 30 kV, and a dose amount is, for example, 2×10¹⁵ions/cm². This ion implantation can be performed, for example, by use ofa focused ion beam device, manufactured by SII NanoTechnology Inc., butthis is not restrictive, and any device may be used as long as beingcapable of performing ion irradiation, which is for example an ionmicroscope or a sample cutting processor. Further, at this time, thegallium ions are not implanted into the device region Rd. Thereby, theimprint mask 1 according to the embodiment is manufactured.

Next described is a method for using the imprint mask 1 according to theembodiment, namely a method for manufacturing a semiconductor deviceaccording to the embodiment.

FIGS. 6A to 6C and FIGS. 7A to 7C are process sectional viewsillustrating the method for manufacturing the semiconductor deviceaccording to the embodiment.

It is to be noted that FIGS. 6A to 6C and FIGS. 7A to 7C show thealignment mark region Ra only at one location for the sake of simplicityof the drawing.

First, as shown in FIG. 6A, a substrate 101 to be processed is prepared.The substrate 101 may, for example, be a silicon wafer, or may also beone obtained by forming an insulating film, a semiconductor film or aconductive film on the silicon wafer. Further, the substrate 101 mayhave already been subjected to some processing. An alignment mark 103 isformed in part of the upper surface of the substrate 101. The alignmentmark 103 on the substrate 101 has a similar pattern to that of thealignment mark 13 of the imprint mask 1, which is for example a patternformed by arranging the concave sections and the convex sections in achecked pattern, but an arrangement cycle of the concave sections is alittle different from that in the alignment mark 13. Next, a resistmaterial 102 is applied over the entire surface of the substrate 101.The resist material 102 is an ultraviolet cure resist material, and hasa refractive index of, for example, 1.4 with respect to the visiblelight. Further, at this stage, the resist material 102 is in a liquid orsemi-liquid state.

Next, as shown in FIG. 6B, above the substrate 101, the imprint mask 1is arranged such that the device pattern 15 and the alignment mark 13turn downward. The imprint mask 1 is then moved toward the substrate101. At this time, visible light VS is applied from above the imprintmask 1, and the alignment mark 13 of the imprint mask 1 and thealignment mark 103 of the substrate 101 are overlapped and detected, toposition the imprint mask 1 with respect to the substrate 101, basedupon a result of the detection. Specifically, by means of an opticaldetection device such as a CCD (Charge Coupled Device) camera, a moiré,which occurs due to a difference between an arrangement cycle of theconcave sections 11 in the alignment mark 13 and an arrangement cycle ofthe concave sections in the alignment mark 103, is detected, to positionthe imprint mask 1 with a margin within several nm. It should be notedthat, since an interface between the quartz plate and the air can beoptically clearly detected at the time before the alignment mark 13coming into contact with the resist material 102, the alignment mark 13can be detected with accuracy. Meanwhile, since the alignment mark 103is one formed on the substrate 101, which is for example the siliconwafer, the mark can be clearly detected.

Then, as shown in FIG. 6C, when the imprint mask 1 is brought closer tothe substrate 101, the imprint mask 1 eventually comes into contact withthe resist material 102. Thereafter, the visible light VS iscontinuously applied from above the imprint mask 1 and the alignmentmark 13 and the alignment mark 103 are overlapped and detected, so thatthe imprint mask 1 is positioned with respect to the substrate 101 whilethe imprint mask 1 is pressed onto the resist material 102. Thereby, theresist material 102 is filled in between the substrate 101 and theimprint mask 1. The imprint mask 1 is then rested with respect to thesubstrate 101.

At this time, assuming that the gallium diffusion layers 16 and 17 (cf.FIG. 3) are not formed in the imprint mask 1, since a refractive indexof the quartz as the material for the imprint mask 1 is almostequivalent to a refractive index of the resist material 102, after thealignment mark 13 coming into contact with the resist material 102, aninterface between the quartz plate 10 and the resist material 102becomes difficult to be optically detected, and the alignment mark 13becomes difficult to be detected. This makes the alignment difficult.

However, in the embodiment, the gallium diffusion layer 16 is formedinside the convex section 12 and the gallium diffusion layer 17 isformed in the region immediately under the concave section 11 in thealignment mark region Ra. The refractive indexes of the galliumdiffusion layers 16 and 17 with respect to the visible light are higherthan the refractive index of the quartz, and at least the galliumdiffusion layer 16 is exposed to the side surfaces of the convex section12. Hence, at least an interface between the side surface of the convexsection 12 and the resist material 102 becomes an interface of two kindsof materials with significantly different refractive indexes, thereby tofacilitate the detection. Therefore, the alignment mark 13 can bedetected with ease. Consequently, in the embodiment, alignment can beperformed with accuracy even after the alignment mark 13 coming intocontact with the resist material 102.

Next, as shown in FIG. 7A, ultraviolet rays UV are applied from abovetoward the resist material 102 through the imprint mask 1, with theimprint mask 1 being in a pressed state onto the resist material 102.Thereby, the resist material 102 is cured and solidified. This resultsin transfer of the device pattern 15 of the imprint mask 1 to the resistmaterial 102, to form a resist pattern 104 made of the resist material102.

Next, as shown in FIG. 7B, the imprint mask 1 is moved upward, to beseparated from the resist pattern 104.

Next, as shown in FIG. 7C, processing is performed on the substrate 101with the resist pattern 104 used as a mask. This processing may, forexample, be etching or implantation of the impurities. For example, inthe case of the substrate 101 being a silicon wafer, performing dryetching with the resist pattern 104 used as the mask can selectivelyremove an upper layer portion of the substrate 101 to form a groove.Alternatively, selectively implanting the impurities with the resistpattern 104 used as the mask can form an impurity diffusion layer in theupper layer portion of the substrate 101. Alternatively, in the case ofthe substrate 101 being one obtained by forming an insulating film and aconductive film on a silicon wafer, performing dry etching with theresist pattern 104 used as the mask can form a groove or a hole in theinsulating film, or process the conductive film into wiring. In thismanner, the semiconductor device is manufactured.

Next, effects of the embodiment are described.

In the imprint mask 1 according to the embodiment, gallium is containedin the convex section 12 of the alignment mark region Ra. Further,gallium is also contained in the portion corresponding to the regionimmediately under the concave section 11 in the quartz plate 10.Accordingly, in the alignment mark region Ra, the refractive index ofthe quartz plate 10 with respect to the visible light is higher than inthe case of gallium being not contained, and the difference inrefractive index from the resist material 102 is large. As a result, asshown in FIG. 6C, the alignment mark 13 can be optically detected withease even after the alignment mark 13 has come into contact with theresist material 102, to facilitate alignment of the imprint mask 1. Thiscan result in accurate positioning of the imprint mask 1 with respect tothe substrate 101.

In contrast, when the imprint mask not containing gallium is used in thealignment mark region, since the refractive index of the quartz isalmost equivalent to that of the resist material, the alignment becomesdifficult after the alignment mark coming into contact with the resistmaterial. For this reason, in the process of pressing the imprint maskonto the resist material, it is necessary to complete the alignmentbefore the imprint mask coming into contact with the resist material andthen press the imprint mask onto the resist material so as to preventdisplacement as much as possible. However, vertical movement of theimprint mask in the pressing process inevitably causes occurrence of thedisplacement. It is thus difficult to obtain sufficient alignmentaccuracy at the time when pressing of the imprint mask is completed,causing deterioration in manufacturing yield of the semiconductordevice. In one example, an alignment accuracy of 8 to 10 nm is obtainedin the case of using the imprint mask not containing gallium, whereasaccording to the embodiment, an alignment accuracy of 6 nm can berealized. It should be noted that in the case of forming a pattern witha half pitch of 22 nm, allowable alignment accuracy is about 7 mm.

Further, in the embodiment, the concentration profile of gallium has apeak inside the convex section 12 in the thickness direction of thequartz plate 10. Hence, it is possible to efficiently arrange gallium,having been introduced into the quartz plate 10, inside the convexsection 12, so as to obtain a large effect with a small amount ofgallium.

Moreover, in the embodiment, the chromium film 21 is removed from thetop of the quartz plate 10, and the imprint mask 1 is made up only ofthe quartz plate 1. Therefore, the imprint mask 1 remains unchanged interms of the configuration thereof even when repeatedly cleaned, andthus has excellent resistance characteristics to cleaning. In contrast,when an imprint mask is configured by coating the quartz plate withanother material such as a chromium film, the coated material comes todisappear every time the imprint mask is cleaned, whereby it isdifficult to hold the characteristics of the imprint mask immediatelyafter manufacturing.

In the method for manufacturing the imprint mask according to theembodiment, in the process shown in FIG. 5C, gallium is ion-implanted tobe introduced into the alignment mark region Ra of the quartz plate 10.At this time, the implantation depth of gallium is made smaller than thedepth of the etching shown in FIG. 5A. This can make a large portion ofgallium, having been implanted into the upper surface 12 a, remaininside the convex section 12, so as to efficiently form the galliumdiffusion layer 16 inside the convex section 12. Further, with thegallium diffusion layer 16 being exposed on the side surfaces of theconvex section 12, the side surfaces of the convex section 12 can beclearly detected when the alignment mark 13 comes into contact with theresist material 102, so as to improve the alignment accuracy.

Further, in the embodiment, gallium is implanted only into the alignmentmark region Ra, and not implanted into the device region Rd. This allowsefficient use of a small amount of gallium, to obtain the foregoingeffect. It is consequently possible to suppress the cost and timerequired for ion-implantation of gallium. Moreover, it is possible toavoid deterioration in transmittance of the ultraviolet ray in thedevice region Rd.

According to the method for manufacturing the semiconductor device inthe embodiment, as described above, it is possible to enhance thealignment accuracy of the imprint mask 1, so as to improve a yield ofthe semiconductor device. This can result in reduction in manufacturingcost of the semiconductor device. The method for manufacturing thesemiconductor device according to the embodiment is applicable, forexample, to a critical layer of the semiconductor device, namelyprocessing of a layer having the finest processing dimension. As oneexample thereof, the method is applicable to formation of an active areaof an NAND flash memory.

Next, a test example of the embodiment is described.

In the test example, conditions for implanting the gallium ions weredecided by the following procedure.

FIG. 8 is a graph with a dose amount of the gallium ions taken on thehorizontal axis and a refractive index of the visible light and atransmittance of the ultraviolet ray taken on the vertical axes,illustrating the relation between an introduction amount of gallium andoptical characteristics of the quartz plate. FIG. 9 is a graph with anacceleration voltage of the ions taken on the horizontal axis and animplantation depth of the ions taken on the vertical axis, illustratingthe relation between the acceleration voltage of the ions and theimplantation depth in the quartz.

It is to be noted that the refractive index of the visible light and thetransmittance of the ultraviolet ray shown on the vertical axes of FIG.8 are represented by relative values with the case of not introducinggallium regarded as one.

As shown in FIG. 8, when the dose amount of gallium increases, therefractive index of the quartz introduced with gallium with respect tothe visible light increases, and the transmittance with respect to theultraviolet ray decreases. That is, the dose amount of gallium ispreferably large for increasing the refractive index of the quartz toincrease the difference from the refractive index of the resist materialso as to make the alignment mark recognizable, whereas the dose amountof gallium is preferably small for ensuring an amount of irradiation ofthe ultraviolet rays required for curing the resist material. Hence, thedose amount of gallium is required to be a value in a range satisfyingboth requirements for the refractive index with respect to the visiblelight and the transmittance with respect to the ultraviolet ray.

In the test example, the transmittance of the quartz plate 10 withrespect to the ultraviolet ray, which is required for curing the resistmaterial on practical conditions, was set to 80% of a quartz plate notintroduced with gallium. In this case, the dose amount of the galliumions is 2×10¹⁵ ions/cm². Further, as shown in FIG. 8, with this doseamount, the refractive index of the quartz with respect to the visiblelight increases up to 128% of the refractive index of the quartz notintroduced with gallium, whereby it is possible to obtain a refractiveindex sufficient at the time of the alignment. Accordingly, the doseamount of the gallium ions was set to 2×10¹⁵ ions/cm².

Further, as shown in FIG. 9, when the acceleration voltage of ionsincreases, the implantation depth increases in almost proportionthereto. The implanted impurities are almost normally distributed alongthe thickness direction of the quartz plate with a positioncorresponding to this implantation depth regarded as the center.Therefore, in order to efficiently implant the impurities into theconvex section 12, the implantation depth is preferably made smallerthan the etching depth of the concave section 11. In particular, makingthe implantation depth of the impurities half the etching depth canlocate the peak of the impurity profile at the center of the convexsection 12 in the thickness direction, so as to effectively introducethe impurities into the convex section 12.

In the test example, the etching depth, namely the depth of the concavesection 11, was set to 50 nm. It is therefore preferable to set theimplantation depth of gallium to 25 nm. From FIG. 9, the accelerationvoltage is required to be set to about 30 kV for making the implantationdepth of gallium 25 nm. The acceleration voltage of gallium was thus setto 30 kV.

Next, a second embodiment is described.

FIG. 10 is a sectional view illustrating an alignment mark region of animprint mask according to the embodiment.

As shown in FIG. 10, an imprint mask 2 according to the embodiment isdifferent as compared with the imprint mask 1 (cf. FIG. 3) according tothe foregoing first embodiment in that a gallium diffusion layer is notformed in the portion corresponding to the region immediately under theconcave section 11 while a gallium diffusion layer 18 is formed insidethe convex section 12 in the quartz plate 10. As with the galliumdiffusion layers 16 and 17 (cf. FIG. 3) in the foregoing firstembodiment, the gallium diffusion layer 18 is a layer which is formed ofquartz as a base material and contains gallium, and is formed integrallywith other portions in the quartz plate 10. Configurations other thanthe above in the imprint mask 2 are similar to those in the imprint mask1 according to the foregoing first embodiment.

Next, a method for manufacturing an imprint mask according to theembodiment is described.

FIGS. 11A to 11D are process sectional views illustrating the method formanufacturing the imprint mask according to the embodiment.

First, the foregoing processes shown in FIGS. 4A to 4D are implemented,to form the chromium film 21 patterned on the quartz plate 10.

Next, as shown in FIG. 11A, the gallium ions are implanted from aboveinto the alignment mark region Ra (cf. FIG. 1) of the quartz plate 10.At this time, an acceleration voltage of the gallium ions is set to sucha value with which at least part of the gallium ions reach the quartzplate 10 through the chromium film 21. Thereby, in the region where thechromium film 21 remains, the gallium ions are implanted into the quartzplate 10 through the chromium film 21. On the other hand, in the regionwhere the chromium film 21 has been removed, the gallium ions aredirectly implanted into the quartz plate 10.

Consequently, as shown in FIG. 11B, in the uppermost layer of the quartzplate 10 in the region where the chromium film 21 remains, the galliumdiffusion layer 18 is formed. On the other hand, in the region where thechromium film 21 has been removed, a gallium diffusion layer 19 isformed at a position deeper than the gallium diffusion layer 18. This isbecause the gallium ions having passed through the chromium film haslost energy and can reach only a thin portion of the quartz plate 10.

Next, as shown in FIG. 11C, dry etching is performed with the chromiumfilm 21 used as the mask, to etch the quartz plate 10. Thereby, thequartz plate is selectively removed in the region where the chromiumfilm 21 has been removed, to form a concave section in the upper surfaceof the quartz plate 10. This results in formation of the device pattern15 and the alignment mark 13. At this time, the depth of the dry etchingis made larger than the introduction depth of the gallium ions in theprocess shown in FIG. 11A, namely the formation depth of the galliumdiffusion layer 19. The gallium diffusion layer 19 is thereby removed bythe dry etching along with the quartz. On the other hand, the galliumdiffusion layer 18 is not removed since being formed in the regionimmediately under the chromium film 21. This results in formation of thegallium diffusion layer 18 inside the convex section 12 and no formationof the gallium diffusion layer in the region immediately under theconcave section 11. Thereafter, the device pattern and the alignment areinspected and corrected.

It is to be noted that, since gallium introduced into the quartz plate10 is continuously distributed in the thickness direction of the quartzplate 10, gallium introduced into the region immediately under theconcave section 11 may not be completely removed even when the depth ofthe dry etching is made larger than the introduction depth of thegallium ions. Also in this case, a content of gallium in the portioncorresponding to the region immediately under the concave section 11 inthe quartz plate 10 is smaller than a content of gallium in the convexsection 12 and the portion corresponding to the region immediatelythereunder in the quartz plate 10.

Next, as shown in FIG. 11D, the chromium film 21 is removed. In such amanner, the imprint mask 2 according to the embodiment is manufactured.A manufacturing method other than the above in the embodiment is similarto that in the foregoing first embodiment. Further, a method formanufacturing a semiconductor device according to the embodiment issimilar to that in the foregoing first embodiment except for the use ofthe imprint mask 2.

Next, effects of the embodiment are described.

In the imprint mask 2 according to the embodiment, in the alignment markregion Ra, gallium is contained in the convex section 12, but gallium isnot contained in the region immediately under the concave section 11. Asdescribed above, the transmittance of light changes when impurities areintroduced into the quartz, and for example when gallium is introduced,the transmittance of the visible light decreases. For this reason, thetransmittance of the visible light in the thickness direction of thequartz plate 10 is lower in the region corresponding to the convexsection 12 than the region corresponding to the concave section 11.Thereby, when the alignment mark 13 is observed by means of the visiblelight reflected by the substrate 101 in the processes shown in FIGS. 6Band 6C, a contrast is formed between the concave section 11 and theconvex section 12. This can result in further facilitating detection ofthe alignment mark 13.

That is, in the foregoing first embodiment, the refractive index of thequartz plate 10 in the alignment mark region Ra was made different fromthe refractive index of the resist material 102, to facilitate detectionof the interface between the quartz plate 10 and the resist material102, and the position of the imprint mask 1 with respect to the quartzplate 101 was then detected through use of phase modulation between thealignment mark 13 and the alignment mark 103. In contrast, in theembodiment, on top of this effect of the first embodiment, thetransmittance of light is made different between the concave section 11and the convex section 12 to make the alignment mark 13 usable as anintensity modulation lattice, so as to further improve the accuracy ofthe alignment mark. The effects in the embodiment other than the aboveare similar to those in the foregoing first embodiment.

Next, a test example of the embodiment is described.

In the test example, conditions for implanting the gallium ions weredecided by the following procedure.

FIG. 12A is a sectional view illustrating a sample of the test example,and FIG. 12B is a graph with a depth of the chromium film from the uppersurface taken on the horizontal axis and a gallium concentration takenon the vertical axis, illustrating a gallium concentration profile alonga straight line B shown in FIG. 12A.

As shown in FIG. 11B, in the region where the chromium film 21 has beenremoved, namely the region where the quartz plate 10 is exposed, it isnecessary that the implantation depth of the gallium ions does notexceed a predetermined etching depth of the quartz plate 10 in theprocess shown in FIG. 11C. This is because, when the implantation depthof the gallium ions exceeds the predetermined etching depth, a largeportion of the gallium diffusion layer cannot be removed by the etching.Hence an upper limit of the acceleration voltage of the gallium ions isdecided based upon the etching depth. Meanwhile, in the region where thechromium film 21 remains, it is necessary that at least part of thegallium ions pass through the chromium film 21 to reach the quartz plate10. Hence a lower limit of the acceleration voltage of the gallium ionsis decided based upon a film thickness of the chromium film 21.

In the test example, the etching depth, namely the depth of the concavesection 11, was set to 50 nm. In this case, the upper limit of theacceleration voltage of the gallium ions is about 40 kV. Meanwhile, thelower limit of the acceleration voltage can be estimated as follows. Asshown in FIG. 12A, a case was assumed where the gallium ions wereimplanted into a sample 51, with the film thickness of the chromium film21 set to 10 nm, at the acceleration voltage set to 15 kV and in thedose amount set to 6×10¹⁵ ions/cm², and a gallium concentration insidethe sample 51 was calculated by simulation. The result is shown in FIG.12B. The vertical axis of FIG. 12B indicates the number of atoms ofgallium existing in each layer when the sample 51 is divided into aplurality of layers each having a thickness of 1 nm.

As shown in FIG. 12B, a peak of the gallium concentration profile islocated at a depth of about 6 nm, and this position corresponds to theinside of the chromium film 21. That is, in this sample, a large portionof gallium atoms remains inside the chromium film 21, and it cannot besaid that the gallium atoms were efficiently implanted into the quartzplate 10. In this case, when the film thickness of the chromium film 21is set to smaller than 6 nm, which is for example not larger than 5 nm,the peak of the gallium concentration profile is located inside thequartz plate 10, and gallium is therefore efficiently implanted into thequartz plate 10. On the contrary, when the film thickness of thechromium film 21 is set to 5 nm, the lower limit of the accelerationvoltage is about 15 kV. According to the above results, the imprint maskaccording to the second embodiment can be manufactured when the etchingdepth is set to not smaller than 50 nm, the film thickness of thechromium film 21 set to not larger than 5 nm, and the accelerationvoltage of the gallium ions set to 15 to 40 kV,

Further, the dose amount of gallium ions can be decided by the followingprocedure.

In the gallium-ion implanting process shown in FIG. 11A, when the doseamount of gallium ions is excessively small, the refractive index andthe transmittance of the convex section 12 cannot be changed to thedegrees required for the alignment. Hence the lower limit of the doseamount of gallium ions is decided based upon the refractive index andthe transmittance that the convex section 12 is required to have. On theother hand, when the dose amount of gallium ions is excessively large,the chromium film 21 is sputtered, to become thinner, and becomes unableto be used as the mask in the etching process shown in FIG. 11C. Hencethe upper limit of the dose amount of gallium ions is decided based uponan initial film thickness of the chromium film 21 and the accelerationvoltage of the gallium ions. As thus described, it is necessary todecide an optimal value of the dose amount of gallium ions inconsideration of the balance between the optical characteristics of theconvex section 12 which are required at the time of the alignment andthe resistance characteristics which are required at the time of the dryetching.

In the test example, when the acceleration voltage of the gallium ionswas set to 30 kV and the dose amount was set to 1×10¹⁶ ions/cm², thefilm thickness of the chromium film 21 decreased by about 2 nm with thision implantation. Therefore, in the case of implanting the gallium ionson these conditions, the initial film thickness of the chromium film 21may be made not smaller than a film thickness obtained by adding 2 nm tothe film thickness required as the mask for etching.

Next, a third embodiment is described.

FIG. 13 is a sectional view illustrating an alignment mark region of animprint mask according to the embodiment.

As shown in FIG. 13, an imprint mask 3 according to the embodiment isdifferent as compared with the imprint mask 2 (cf. FIG. 10) according tothe foregoing second embodiment in that a mixing layer 20 is formed inthe upper most layer of the convex section 12 in the quartz plate 10. Inthe mixing layer 20, chromium, silicon, oxygen and gallium arecontained. Inside the mixing layer 20, a composition is inclined in thethickness direction, and in a portion excluding a gallium concentrationin the composition of the mixing layer 20, a chromium concentrationbecomes higher in an ascending direction, while a silicon concentrationand an oxygen concentration become higher in a descending direction. Thegallium diffusion layer 18 is provided under the mixing layer 20 in theconvex section 12, and the mixing layer 20 is in contact with thegallium diffusion layer 18. Configurations other than the above in theimprint mask 3 are similar to those in the imprint mask 2 according tothe foregoing second embodiment.

Next, a method for manufacturing the imprint mask according to theembodiment is described.

FIGS. 14A to 14D are process sectional views illustrating the method formanufacturing the imprint mask according to the embodiment.

First, the foregoing processes shown in FIGS. 4A to 4D are implemented,to form the chromium film 21 patterned on the quartz plate 10. However,the film thickness of the chromium film 21 is made smaller than that inthe foregoing second embodiment, which is for example not larger than 5nm.

Next, as shown in FIG. 14A, the gallium ions are implanted from aboveinto the alignment mark region Ra (cf. FIG. 1) of the quartz plate 10.At this time, the acceleration voltage of the gallium ions is madehigher than in the foregoing second embodiment, which is for example 40kV. This leads to occurrence of a mixing phenomenon between the chromiumfilm 21 and the quartz plate 10. This mixing phenomenon is a phenomenonwhich occurs because implantation of the gallium ions causes chromiumatoms constituting the chromium film 21 to be pressed into the quartzplate 10 on an interface between the chromium film 21 and the quartzplate 10, and silicon atoms and oxygen atoms constituting the quartzplate 10 to bounce inside the chromium film 21.

Thereby, as shown in FIG. 14B, the mixing layer 20 is formed in theuppermost layer of the quartz plate 10 in the region where the chromiumfilm 21 remains, and the gallium diffusion layer 18 is formed in aregion immediately thereunder. That is, in the region where the chromiumfilm 21 remains, the chromium film 21, the mixing layer 20 and thegallium diffusion layer 18 are arrayed in this order downward fromabove. In the embodiment, the mixing layer 20 is defined as a layer atleast containing chromium, silicon and oxygen. On the contrary, siliconand oxygen are defined not to be substantially contained in the chromiumfilm 21, and chromium should not be substantially contained in thegallium diffusion layer 18. Further, gallium may be contained in thechromium film 21 and the mixing layer 20.

Meanwhile, in the region where the chromium film 21 has been removed,the gallium diffusion layer 19 is formed at a deeper position than thegallium diffusion layer 18. Further, the mixing film is not formed inthis region since the chromium film 21 does not remain therein.

Next, as shown in FIG. 14C, dry etching is performed with the chromiumfilm 21 used as a mask and fluorine-based gas such as methanetetrafluoride (CF₄) gas used as etching gas, to etch the quartz plate10. Thereby, the quartz plate is selectively removed, to form a concavesection in the upper surface of the quartz plate 10. At this time, thedepth of the dry etching is made larger than the introduction depth ofthe gallium ions in the process shown in FIG. 14A. Thereby, the galliumdiffusion layer 19 is removed by the dry etching along with the quartz.

Next, as shown in FIG. 14D, the chromium film 21 is removed. At thistime, the upper portion of the mixing layer 20 may be removed along withthe chromium film 21, but at least the lower portion of the mixing layer20, namely the portion where the chromium atoms have been implanted intothe quartz plate 10 remains. In such a manner, the imprint mask 3according to the embodiment is manufactured. A manufacturing methodother than the above in the embodiment is similar to that in theforegoing second embodiment. Further, a method for manufacturing asemiconductor device according to the embodiment is similar to that inthe foregoing first embodiment except for the use of the imprint mask 3.

In the embodiment, in the alignment mark region Ra of the imprint mask3, the mixing layer 20 is formed inside the convex section 12, togetherwith the gallium diffusion layer 18. The mixing layer 20 has a lowtransmittance of the visible light since containing chromium as a metalelement. For this reason, a higher contrast can be realized in thealignment mark 13. This further improves the alignment accuracy at thetime of imprinting.

In addition, it is considered that the foregoing mixing phenomenon alsooccurs in the foregoing second embodiment, but in the embodiment, thefilm thickness of the chromium film 21 is made smaller to increase theacceleration voltage of the gallium ions so that the mixing phenomenonis positively used. With the acceleration voltage of the gallium ionsincreased, kinetic energy of the gallium ions increases, to make themixing apt to occur. Further, with the initial film thickness of thechromium film made smaller, a loss of energy is suppressed at the timeof passage of the gallium ions through the chromium film, to make themixing apt to occur.

Further, in the embodiment, it is also considered that part of thechromium film 21 may disappear by sputtering in the gallium-ionimplanting process shown in FIG. 14A, due to the initial film thicknessof the chromium film 21 being small. However, also in this case, themixing layer 20 containing chromium is hardly etched when dry etching isperformed by means of fluorine-based etching gas. Therefore, in theprocess of etching the quartz plate 10 which is shown in FIG. 14C, themixing layer 20 can be used as a mask.

Next, the test example of the embodiment is described.

FIG. 15A is a sectional view illustrating a sample of the test example,and FIG. 15B is a graph with a depth of the chromium film from the uppersurface taken on the horizontal axis and an atomic concentration ratiotaken on the vertical axis, illustrating a profile of a compositionalong a straight line C shown in FIG. 15A.

It is to be noted that FIG. 15B shows a value obtained by convertingconcentrations of silicon and oxygen into that of silicon oxide (SiO₂).

As shown in FIG. 15A, in the test example, a case was assumed where asample 52, formed with the chromium film 21 having a film thickness of10 nm on the quartz plate 10, was irradiated with beams of the galliumions from above the chromium film 21, to form the mixing layer 20. Theacceleration voltage of the gallium ions was set to 15 kV. Then, thenumber of atoms with respect to each 1-nm depth in a 1-cm square regionseen from above was calculated by simulation, to create the profileshown in FIG. 15B.

As shown in FIG. 15B, silicon and oxygen are not substantially containedin the uppermost layer of the sample 52. Further, concentrations ofsilicon and oxygen monotonously increase as the positions thereof becomedeeper from a depth of 6 nm to a depth of 10 nm, and monotonouslydecrease as the positions thereof become deeper from the depth of 10 nmto a depth of 21 nm. On the other hand, a concentration of chromiummonotonously decreases as the position thereof becomes deeper from theuppermost layer to the depth of 21 nm. It is thereby found that the filmthickness of the chromium film 21 decreases to about 6 nm due toimplantation of the gallium ions. Further, it is found that the mixinglayer 20 is formed at a position at least from a depth of about 6 nm toa depth of about 21 nm.

Next, a fourth embodiment will be described.

The configuration of an imprint mask according to the embodiment issimilar to the imprint mask 2 (see FIG. 10) according to the foregoingsecond embodiment.

A method for manufacturing an imprint mask according to the embodimentwill be described hereinafter.

FIGS. 16A to 16E are process sectional views illustrating the method formanufacturing the imprint mask according to the embodiment.

First, as shown in FIG. 16A, the quartz plate 10 is prepared and thechromium film 21 is formed on the quartz plate 10. At this time, aposition of a region where the alignment mark 13 is to be formed on thequartz plate 10 is previously determined. The position of the region,for example, can be determined by a distance or the like from a cornerof the quartz plate 10.

Next, gallium ions are implanted into this region. Thereby, as shown inFIG. 16B, the gallium ions are implanted into the quartz plate 10through the chromium film 21 to form the gallium diffusion layer 18 inthe uppermost layer of the quartz plate 10, namely, the region being incontact with the chromium film 21. The implantation condition of thegallium ions can be determined, for example, by the process similar tothe test example (see FIGS. 12A and 12B) of the foregoing secondenvironment. That is, the lower limit of the acceleration voltage of thegallium ions is set to such a value with which the gallium ionspenetrate through the chromium film 21 and the upper limit of theacceleration voltage of the gallium ions is set to such a value withwhich the implantation depth of the gallium ions does not exceed anetching depth. In the embodiment, for example, a film thickness of thechromium film 21 is set to approximate 5 nm and the acceleration voltageis set to 15 to 40 kV. The lower limit of the dose amount of the galliumions is set to such a value with which the refractive index and thetransmittance of the convex section 12 can be varied sufficiently, theupper limit of the dose amount is set to such a value with which thechromium film 21 is made to remain sufficiently as an etching mask.

Next, as shown in FIG. 16C, the chromium film 21 is patterned. Thispatterning is performed, for example as described in the foregoing firstembodiment, by applying an electron-beam resist film on the chromiumfilm 21, performing electron-beam lithography, developing theelectron-beam resist film, and dry-etching the chromium film 21 usingthe patterned electron-beam resist film as a mask, for example, withchlorine-based gas. Alternatively, a resist pattern is directly formedusing a replica template replication device for high volume productionand the chromium film 21 may be dry-etched using this resist pattern asa mask.

Next, as shown in FIG. 16D, the quartz plate 10 is dry-etched withfluorine-based gas such as tetrafluoromethane or the like as an etchinggas using the patterned chromium film 21 as a mask. Thereby, the concavesections 11 are formed on the upper surface of the quartz plate 10 and aportion between the concave sections 11 forms the convex section 12. Atthis time, the etching depth is made larger than the implantation depthof the gallium ions. Thus, the gallium diffusion layer 18 is etched andremoved in a region not covered with the chromium film 21 in the quartzplate 10.

Next, as shown in FIG. 16E, for example, the chromium film 21 is peeledby wet-etching using cerium nitrate. Thus, the alignment mark withcontrast to white light can be formed similar to the foregoing secondembodiment.

In the embodiment, different from the foregoing second and thirdembodiments, the ion implantation process is not performed during thepatterning process. Thereby, possibility of dust attachment to thequartz plate 10 or the like is decreased and process defects can bereduced. The method for manufacturing the imprint mask and the methodfor manufacturing the semiconductor device of the embodiment other thanthe above are similar to those of the second embodiment.

Next, a fifth embodiment will be described.

The configuration of an imprint mask according to the embodiment issimilar to that of the imprint mask 2 (see FIG. 10) according to theforgoing second embodiment.

A method for manufacturing an imprint mask according to the embodimentwill be described.

FIGS. 17A to 17C are process sectional views illustrating the method formanufacturing the imprint mask according to the embodiment.

First, as shown in FIG. 17A, the quartz plate 10 is prepared.Subsequently, the gallium ions are implanted in the quartz plate 10without formation of the chromium film 21. At this time, the ionimplantation is performed at least to the region where the alignmentmark is to be formed. And the acceleration voltage of the ionimplantation is made lower than the case of ion implantation through thechromium film 21 as in the foregoing each embodiment. The implantationdepth of the gallium ions is made to surpass the etching depth performedin a later process. For example, the implantation depth of the galliumions is set shallower than 50 nm. Thereby, as shown in FIG. 17B, thegallium diffusion layer 18 is formed in the uppermost portion of thequartz plate 10.

Next, as shown in FIG. 17C, chromium is deposited, for example, by asputtering method and the chromium film 21 is formed on the quartz plate10.

Subsequent processes are similar to the foregoing fourth embodiment.That is, as shown in FIG. 16C, the chromium film 21 is patterned. Next,as shown in FIG. 16D, using the patterned chromium film 21 as a mask,the quartz plate 10 is etched deeper than the implantation depth of thegallium ions. Thereafter, as shown in FIG. 16E, the chromium film 21 isremoved. Thereby, the imprint mask similar to the foregoing secondembodiment can be manufactured.

According to the embodiment, after implanting the gallium ions in theprocess shown in FIG. 17A, the chromium film 21 is formed in the processshown in FIG. 17C. Thus, it is unnecessary to consider film reduction ofthe chromium film 21 due to a sputtering effect by the gallium ions.Therefore, the upper limit of the dose amount of the gallium ions isrelaxed and the gallium ions can be implanted with required amount toobtain contrast sufficiently.

Further, according to the embodiment, as similar to the foregoing secondembodiment, defects due to dusts can be reduced because the ionimplantation process is not performed during the patterning process. Themethod for manufacturing the imprint mask and the method formanufacturing the semiconductor device in the embodiment other than theabove are similar to the foregoing second embodiment.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the invention.

For example, although the example was shown in the foregoing firstembodiment where the implantation depth of the ions was made half theetching depth, the implantation depth is not restricted to this, and canbe any depth as long as gallium is introduced into the convex section.

Further, although the example was shown in each of the foregoingembodiments where the impurities to be implanted into the quartz plateare gallium, this is not restrictive. The impurities to be implantedinto the quartz plate can be any one as long as making a change in thecomposition of the quartz and may, for example, be one element selectedfrom a group consisting of gallium, xenon, antimony, argon, silicon,nitrogen, and lead. In this case, the acceleration voltage at the timeof the ion implantation can be selected as appropriate in accordancewith the type of the ions.

Moreover, although the example was shown in each of the foregoingembodiments where the chromium film is formed as the mask to be used atthe time of etching the quartz plate, this is not restrictive. This maskcan be any film as long as being able to take an etching selection ratiowith the quartz plate, and is favorably a metal film, for example. Asthe metal film, for example, there can be used a film made up of one ormore metals selected from a group consisting of chromium, tantalum, andruthenium. Alternatively, there may be used a film made up of a compoundof these metals, or a film compositely contained with these metals orthe compound. In this case, these metals are contained in the mixinglayer in the foregoing third embodiment.

Furthermore, although the gallium ions are implanted into the whole ofthe alignment mark region in each of the foregoing embodiments, thegallium ions may be selectively implanted only into a boundary portionbetween the concave section 11 and the convex section 12. In this case,in the imprint mask after manufacturing, a gallium concentration in theportion including the side surfaces of the convex section 12 becomeshigher than a gallium concentration in a central portion of the convexsection 12 seen from above. It is thereby possible to improvecharacteristics of the alignment mark as an object to be detected with asmaller implantation amount of gallium.

According to the embodiments described above, it is possible to realizean imprint mask capable of performing alignment with accuracy, a methodfor manufacturing the same, and a method for manufacturing asemiconductor device.

What is claimed is:
 1. An imprint mask, comprising a quartz plate, thequartz plate having a plurality of concave sections formed in part of anupper surface on the quartz plate, impurities being contained in a firstportion of the quartz plate between the concave sections, and aconcentration profile of the impurities in the first portion and asecond portion corresponding to a region immediately under the firstportion in the quartz plate has a peak inside the first portion in athickness direction of the quartz plate.
 2. The mask according to claim1, wherein the impurities are also contained in a third portioncorresponding to a region immediately under each of the concave sectionsin the quartz plate.
 3. The mask according to claim 1, wherein a contentof the impurities in a third portion corresponding to a regionimmediately under each of the concave sections in the quartz plate issmaller than a content of the impurities in the first portion bet andthe second portion.
 4. The mask according to claim 1, wherein the firstportion contains a metal.
 5. The mask according to claim 4, wherein themetal is one or more metals selected from the group consisting ofchromium, tantalum, and ruthenium.
 6. The mask according to claim 1,wherein the impurities are one element selected from the groupconsisting of gallium, xenon, antimony, argon, silicon, nitrogen, andlead.
 7. The mask according to claim 1, wherein the plurality of concavesections is a first plurality of concave sections in a first part of theupper surface of the quartz plate, the quartz plate further comprises asecond plurality of concave sections in a second part of the uppersurface of the quartz plate, and the impurities are not contained in aportion corresponding to a region immediately under the second part ofthe upper surface of the quartz plate.